/*
 * Tencent is pleased to support the open source community by making Angel available.
 *
 * Copyright (C) 2017 THL A29 Limited, a Tencent company. All rights reserved.
 *
 * Licensed under the BSD 3-Clause License (the "License"); you may not use this file except in
 * compliance with the License. You may obtain a copy of the License at
 *
 * https://opensource.org/licenses/BSD-3-Clause
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 *
 */

package com.tencent.angel.ml.optimizer2.lossfuncs

object LogisticLoss {
  private val threshold = Math.log(Double.MaxValue)

  def apply(ymodel: Double, yture: Double): Double = {
    val temp = -yture * ymodel
    if (temp > threshold) {
      temp
    } else {
      Math.log1p(Math.exp(-yture * ymodel))
    }
  }

  def grad(ymodel: Double, yture: Double): Double = {
    val temp = -yture * ymodel
    if (temp > threshold) {
      0.0
    } else {
      -yture / (1.0 + Math.exp(yture * ymodel))
    }

  }
}
